A heat exchanger is constituted, for example, in the following manner: a large number of heat transfer pipes are arrayed within a housing provided therein so as to be formed in a U shape, and are coupled to a lower inlet collection pipe and a upper outlet collection pipe, respectively. An inlet pipe is provided on an upper portion thereof to communicate or connect with the housing, and an outlet pipe is provided on an upper sidewall thereof to be coupled to an intermediate space thereof.
Hence, for example, if cooling water is supplied from the inlet collection pipe into the large number of heat transfer pipes within the housing while high-temperature air is supplied from the inlet pipe into the housing, then the high-temperature air descends and the cooling water ascends in the housing, and thus a heat exchange is performed. Then, the cooled air reverses itself upward from the lower portion of the housing, ascends through the intermediate space, and is discharged from the outlet pipe. Meanwhile, the cooling water is discharged from the outlet collection pipe.
In such a heat exchanger, it is necessary to perform an ECT inspection for the heat transfer pipes periodically. However, because oxide scale is generated on the inner surfaces of the heat transfer pipes due to long-term use, it is necessary to remove this oxide scale before the inspection. As a method for removing the oxide scale on the inner surfaces of the heat transfer pipes, it is general to use a blast method in which an abrasive is sent with pressure to the heat transfer pipes to abrade and remove the scale. For example, this method is disclosed in Japanese Patent Laid-Open Publication 2001-150348.
As described above, in the conventional oxide scale removing method, the swirling flow of the abrasive is made to collide with the oxide scale generated on the inner surfaces of the steel pipes to perform blast processing therefor, thus removing the oxide scale. The oxide scale can be removed irrespective of the unevenness of the inner surfaces of the steel pipes by allowing the abrasive to collide with the oxide scale as described above on the inner surfaces of the steel pipes from various directions. However, regarding a specific portion where a large amount of oxide scale is generated, the removal of the oxide scale cannot be sufficient. In order to remove the large amount of oxide scale generated on the inner surfaces of the steel pipes, the amount of abrasive and a rate or speed at which the abrasive is sent with pressure must be increased, causing problems that an equipment for abrasion is to be larger and that costs become higher.
Moreover, due to restriction on the local thinning amount of the bent portion of each U-shaped pipe, the increases in the abrasive amount and the pressure rate at which the abrasive is sent with pressure may sometimes be limited when the oxide scale is in a large amount. In this case, the oxide scale is removed by a manual operation, causing a problem that it takes an extremely long time to do the operation for the heat exchanger having no less than several thousands of heat transfer pipes.
The present invention was made in order to solve such problems as described above. It is an object of the present invention to provide an apparatus and a method for removing a foreign object or matter, which are capable of easy removal of the foreign object such as scale attached onto inner surfaces of pipes of nuclear power equipment or the like for a short period of time by means of simple equipment and manner.